当尝试将具有双向关联的 JPA 对象转换为 JSON 时，我不断得到
org.codehaus.jackson.map.JsonMappingException: Infinite recursion (StackOverflowError)
我只找到了this thread基本上以建议避免双向关联结束。有没有人知道这个 Spring 错误的解决方法？
-------- 编辑 2010-07-24 16:26:22 --------
代码片段:
业务对象 1:
@Entity
@Table(name = "ta_trainee", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class Trainee extends BusinessObject {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
@Column(name = "id", nullable = false)
private Integer id;
@Column(name = "name", nullable = true)
private String name;
@Column(name = "surname", nullable = true)
private String surname;
@OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@Column(nullable = true)
private Set<BodyStat> bodyStats;
@OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@Column(nullable = true)
private Set<Training> trainings;
@OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@Column(nullable = true)
private Set<ExerciseType> exerciseTypes;
public Trainee() {
super();
}
//... getters/setters ...
}
业务对象 2:
import javax.persistence.*;
import java.util.Date;
@Entity
@Table(name = "ta_bodystat", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class BodyStat extends BusinessObject {
@Id
@GeneratedValue(strategy = GenerationType.TABLE)
@Column(name = "id", nullable = false)
private Integer id;
@Column(name = "height", nullable = true)
private Float height;
@Column(name = "measuretime", nullable = false)
@Temporal(TemporalType.TIMESTAMP)
private Date measureTime;
@ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinColumn(name="trainee_fk")
private Trainee trainee;
}
Controller :
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
import javax.servlet.http.HttpServletResponse;
import javax.validation.ConstraintViolation;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
@Controller
@RequestMapping(value = "/trainees")
public class TraineesController {
final Logger logger = LoggerFactory.getLogger(TraineesController.class);
private Map<Long, Trainee> trainees = new ConcurrentHashMap<Long, Trainee>();
@Autowired
private ITraineeDAO traineeDAO;
/**
* Return json repres. of all trainees
*/
@RequestMapping(value = "/getAllTrainees", method = RequestMethod.GET)
@ResponseBody
public Collection getAllTrainees() {
Collection allTrainees = this.traineeDAO.getAll();
this.logger.debug("A total of " + allTrainees.size() + " trainees was read from db");
return allTrainees;
}
}
实习生DAO的JPA实现:
@Repository
@Transactional
public class TraineeDAO implements ITraineeDAO {
@PersistenceContext
private EntityManager em;
@Transactional
public Trainee save(Trainee trainee) {
em.persist(trainee);
return trainee;
}
@Transactional(readOnly = true)
public Collection getAll() {
return (Collection) em.createQuery("SELECT t FROM Trainee t").getResultList();
}
}
persistence.xml
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"
version="1.0">
<persistence-unit name="RDBMS" transaction-type="RESOURCE_LOCAL">
<exclude-unlisted-classes>false</exclude-unlisted-classes>
<properties>
<property name="hibernate.hbm2ddl.auto" value="validate"/>
<property name="hibernate.archive.autodetection" value="class"/>
<property name="dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
<!-- <property name="dialect" value="org.hibernate.dialect.HSQLDialect"/> -->
</properties>
</persistence-unit>
</persistence>
最佳答案
您现在可以使用 JsonIgnoreProperties 抑制属性的序列化(在序列化期间)，或忽略处理读取的 JSON 属性(在反序列化期间)。如果这不是您要查找的内容，请继续阅读下文。
(感谢 As Zammel AlaaEddine 指出这一点)。
从 Jackson 1.6 开始，您可以使用两个注解来解决无限递归问题，而无需在序列化过程中忽略 getter/setter: @JsonManagedReference 和 @JsonBackReference .
说明
为了让 Jackson 正常工作，关系的两侧之一不应被序列化，以避免导致您的 stackoverflow 错误的无限循环。
因此，Jackson 将引用的前半部分(您在 Trainee 类中的 Set<BodyStat> bodyStats)转换为类似 json 的存储格式；这就是所谓的编码过程。然后，Jackson 查找引用的后面部分(即 BodyStat 类中的 Trainee trainee)并保持原样，而不是对其进行序列化。这部分关系将在前向引用的反序列化(unmarshalling)期间重新构建。
您可以像这样更改您的代码(我跳过了无用的部分):
业务对象 1:
@Entity
@Table(name = "ta_trainee", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class Trainee extends BusinessObject {
@OneToMany(mappedBy = "trainee", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@Column(nullable = true)
@JsonManagedReference
private Set<BodyStat> bodyStats;
业务对象 2:
@Entity
@Table(name = "ta_bodystat", uniqueConstraints = {@UniqueConstraint(columnNames = {"id"})})
public class BodyStat extends BusinessObject {
@ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinColumn(name="trainee_fk")
@JsonBackReference
private Trainee trainee;
现在一切都应该正常工作了。
如果您想了解更多信息，我写了一篇关于 Json and Jackson Stackoverflow issues on Keenformatics 的文章，我的博客。
编辑:
另一个有用的注释是@JsonIdentityInfo :使用它，Jackson 每次序列化您的对象时，都会为其添加一个 ID(或您选择的其他属性)，这样它就不会每次都完全“扫描”它。当您在更多相互关联的对象(例如:Order -> OrderLine -> User -> Order 和一遍遍)之间有一个链式循环时，这可能很有用。
在这种情况下，您必须小心，因为您可能需要多次读取对象的属性(例如，在包含多个共享同一卖家的产品的产品列表中)，而此注释会阻止您这样做所以。我建议始终查看 firebug 日志以检查 Json 响应并查看代码中发生了什么。
来源:
关于java - jackson JSON 和 Hibernate JPA 问题的无限递归，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/3325387/